Our laboratory has been actively studying the pathogenesis of alcoholic liver disease, focusing on the role of acetaldehyde dehydrogenase 2 (ALDH2) and prednisolone in alcoholic liver injury, and we have also developed a mouse model of chronic plus binge ethanol feeding model, which represents early stages of human alcoholic steatohepatitis. Chronic alcohol consumption is a leading cause of chronic liver disease worldwide, leading to cirrhosis and hepatocellular carcinoma. Currently, the most widely used model for alcoholic liver injury is ad libitum feeding with the Lieber-DeCarli liquid diet containing ethanol for 4-6 weeks; however, this model, without the addition of a secondary insult, only induces mild steatosis, slight elevation of serum alanine transaminase (ALT) and little or no inflammation. During this reporting period, we developed a simple mouse model of alcoholic liver injury by chronic ethanol feeding (10-d ad libitum oral feeding with the Lieber-DeCarli ethanol liquid diet) plus a single binge ethanol feeding. This chronic-plus-single-binge ethanol feeding synergistically induces liver injury, inflammation and fatty liver, which mimics acute-on-chronic alcoholic liver injury in patients. Chronic-binge ethanol feeding leads to high blood alcohol levels; thus, this simple model will be very useful for the study of alcoholic liver disease (ALD) and of other organs damaged by alcohol consumption. Aldehyde dehydrogenase 2 (ALDH2) is the major enzyme that metabolizes acetaldehyde produced from alcohol metabolism. Approximately 40 to 50% of East Asians carry an inactive ALDH2 gene and exhibit acetaldehyde accumulation after alcohol consumption. However, the role of ALDH2 deficiency in the pathogenesis of alcoholic liver injury remains obscure. During this reporting period, we have used wild-type (WT) and ALDH2-/- mice to examine the roles of ALDH2 in alcoholic liver injury and fibrosis by using ethanol feeding and/or carbon tetrachloride (CCl4) treatment. Compared with WT mice, ethanol-fed ALDH2-/- mice had higher levels of malondialdehyde and acetaldehyde (MAA) adduct and greater hepatic inflammation, with higher hepatic interleukin-6 (IL-6) expression but surprisingly lower levels of steatosis and serum ALT. Higher IL-6 levels were also detected in ethanol-treated precision-cut-liver slices from ALDH2-/- mice and in Kupffer cells isolated from ethanol-fed ALDH2-/- mice than those levels in WT mice. In vitro incubation with MAA enhanced the LPS-mediated stimulation of IL-6 production in Kupffer cells. In agreement with these findings, hepatic activation of the major IL-6 downstream signaling molecule signal transducer and activator of transcription 3 (STAT3) was higher in ethanol-fed ALDH2-/- mice than in WT mice. An additional deletion of hepatic STAT3 resulted in increased steatosis and hepatocellular damage in ALDH2-/- mice. Finally, ethanol-fed ALDH2-/- mice were more prone to CCl4-induced liver inflammation and fibrosis than ethanol-fed WT mice. CONCLUSIONS: ALDH2-/- mice are resistant to ethanol-induced steatosis but prone to inflammation and fibrosis via MAA-mediated paracrine activation of IL-6 in Kupffer cells. These findings suggest that ALDH2-deficient individuals may be resistant to steatosis, but are prone to liver inflammation and fibrosis following alcohol consumption. Prednisolone is a corticosteroid that has been used to treat inflammatory liver diseases, such as autoimmune hepatitis and alcoholic hepatitis. However, the results have been controversial, and how prednisolone affects liver disease progression remains unknown. During this reporting period, we examined the effect of prednisolone treatment on several models of liver injury, including T/NKT cell hepatitis induced by concanavalin A (Con A) and -galactosylceramide (-GalCer), and hepatotoxin-mediated hepatitis induced by carbon tetrachloride (CCl4). Prednisolone administration attenuated ConA- and -GalCer-induced hepatitis and systemic inflammatory responses. Treating mice with prednisolone also suppressed inflammatory responses in a model of hepatotoxin (CCl4)-induced hepatitis, but surprisingly exacerbated liver injury and delayed liver repair. Immunohistochemical and flow cytometric analyses demonstrated that prednisolone treatment inhibited hepatic macrophage and neutrophil infiltration in CCl4-induced hepatitis and suppressed their phagocytic activities in vivo and in vitro. Macrophage and/or neutrophil depletion aggravated CCl4-induced liver injury and impeded liver regeneration. Finally, conditional disruption of glucocorticoid receptor in macrophages and neutrophils abolished prednisolone-mediated exacerbation of hepatotoxin-induced liver injury. Conclusion: Prednisolone treatment prevents T/NKT cell hepatitis but exacerbates hepatotoxin-induced liver injury by inhibiting macrophage- and neutrophil-mediated phagocytic and regenerative functions. These findings may not only increase our understanding of the steroid treatment mechanism but also help us to better manage steroid therapy in liver diseases. In addition, we are also collaborating with Drs. George Kunos and Pal Pacher from NIAAA to investigate the role of the endocannabinoid system in alcoholic liver disease.